1. Technical Field
This invention relates to methods for predicting the performance of a motor vehicle under specified conditions, and more particularly to a method for determining the tractive effort required to propel a vehicle at a given speed under a given set of conditions, to thereby aid designers and engineers in predicting the performance of various engine, drive train and aerodynamic configurations of a vehicle during design and testing of the vehicle.
2. Discussion
Often the design engineer and management are faced with difficult/design questions in choosing the proper performance parameters of a new vehicle. Some performance factors to be considered are whether the engine to be used is capable of providing enough power for the tasks which the vehicle will be expected to perform. Such tasks might include towing trailers, boats or other items, traveling frequently in geographic areas where steep grades are frequently encountered or in areas where the altitude may affect the performance of the vehicle engine.
Other factors that the design engineer must consider are the transmission ratios and whether these selected ratios will allow easy, positive engagement in shifting of the transmission under various driving conditions. The engineer must also consider the rear axle ratio and whether the same has been properly selected for the anticipated road and operating conditions which the vehicle will experience.
Still other factors that the designer must consider are the gross vehicle weight (i.e., the weight of the vehicle plus the additional weight "seen" by the vehicle if the vehicle is towing a trailer) and what impact the gross vehicle weight may have on the maximum vehicle speed on various surfaces having various grades. Closely connected with this consideration is whether or not the engine to be used in the vehicle will be powerful enough to provide sufficient power to move the vehicle under all of the wide ranging conditions that the vehicle may be expected to encounter. It would also be helpful for the designer to be able to predict whether a particular transmission, transfer case or axle will perform adequately when packaged with an engine having a particular displacement.
When designing a vehicle, it would also be helpful to be able to predict if the cooling and climate control components anticipated to be used with the vehicle will be sufficient under all of the conditions that one anticipates the vehicle will be used in. Accordingly, a tool which allows the engineer to predict if the components anticipated to be used will be adequate under anticipated driving conditions, and which allows the engineer to establish the working point of the engine or the transmission would be extremely helpful. In particular, a tool which allows the engineer to predict the rejected heat by the vehicle engine, the rejected heat by the vehicle transmission, the fan RPM, the engine RPM and the coolant flow from the water pump would be extremely helpful in predicting whether the cooling and climate control components will be sufficient to perform under strenuous operating conditions that the vehicle may experience when in use.
In view of the foregoing it would therefore be highly desirable to provide a method for determining, based on a variety of input data entered by an engineer or designer, and before assembling and testing of any particular test vehicle, the traction force required at the wheels of a vehicle in order to operate the vehicle under a variety of predetermined conditions and at a variety of designated vehicle speeds. This would allow the vehicle engineer or designer to determine the traction force that will be needed at the wheels of the vehicle at various operating speeds when taking into account a wide variety of parameters such as engine displacement, drivetrain components, ambient temperatures, etc., and to enable the designer or engineer to better predict the needed vehicle configuration to meet the anticipated driving conditions.